1. Field of the Invention
The present invention is in the field of medical technology and information technology, and in particular concerns an approach in order to register image data from different image series in order to associate these with one another and to be able to present or process these images on a monitor in synchronization.
2. Description of the Prior Art
In examinations known as multi-region magnetic resonance tomographic examinations, for which measures are executed for different body regions at different points in time, the problem is presented of structuring the multiple acquired image data sets so that they can be presented on a monitor synchronously, and thus so as to be cognitively evaluable by an assessor.
However, in addition to the mere presentation of images, image registration is also required for many different image calculations, processings and evaluations. If, for example, it is desirable to offset a series from the current examination and a series from a previous examination with respect to one another, these series must be registered with each other (brought into registration). The “offsetting” can extend from a simple image subtraction to complex statistical contrast variation calculations or tumor growth calculations. In principle, two-dimensional or three-dimensional acquisitions of the human body or of specific body parts, organs or tissue structures are generated within the scope of the image acquisition (for example with the modalities MRT, CT, PET, etc.). In order to enable an overview of the chronological development of the body structures (for example of tumor tissue) in the acquired image data, these acquisitions are normally repeated at a later point in time. In the assessment of these exposures, the radiologist would typically like to consider the current image data together with specific or selected available images from pre-examinations so that he or she can better assess anatomical or pathological variations.
Many different finding systems (normally software-based) are presently operated with which a finding based on different image data of different series should be executed. For this purpose, current image data sets must be associated and registered with image data sets of prior examinations in order to present these synchronously. The image registration includes a transformation of the spatial coordinates of a first image with those of the second image. Depending on the type of acquisition method or the modality that is used, the image registration is a necessarily complex task. In contrast to CT or PET examinations in which only a few image volumes with respective large spatial coverage are normally created, in MR examinations (“magnetic resonance tomography”) a number of smaller image volumes are normally acquired. Depending on the examination, up to 30-40 image volumes can be produced. The problem is then presented that the “correct” image data of the prior examination must be combined with the respective “correct” image data of the current examination.
In the prior art, known software-based solutions for the image registration task described in the preceding are normally based on an automatic image registration, and apply one of the following strategies for image registration.
1. A representative series (image volume) of a current examination is registered with a representative series of the previous examination. The series that best (as extensively as possible) characterizes the properties of all image volumes of the respective study is typically defined as a representative series. An explicit registration is then executed between the representative series of the current examination and the representative series of the previous examination. All remaining registrations between the two series (previous examination and current examination) can then be calculated via implicit identity registrations. However, this approach leads to a limited registration precision in the peripheral body regions. Therefore, this approach is not applicable to multi-region MR examinations, or can only be applied with quality losses.
2. All possible combinations of image data sets are combined. In this approach all series pairs are registered with one another for which a synchronized presentation or processing could potentially be required. This approach is based on the “Small World Phenomenon” and is extremely computationally intensive, and therefore time-consuming. Moreover, the approach has the disadvantage that it is not applicable in multi-region MR examinations since here multiple body regions of the patient are scanned, and thus image data sets of multiple studies (that for their part comprise multiple series) are acquired, which overall makes the combination job still more complex in its design.
An additional disadvantage of the first approach is that a representative series with sufficient spatial coverage must be determined for both the current examination and for the previous examination. In contrast to computed tomography, no such representative series (that, moreover, has a sufficient registration precision) is normally found in multi-region magnetic resonance tomography. This is based on the physical fact that, given an MR examination with sufficient spatial coverage, the examination is normally executed over a long period of time, which in turn limits the registration precision because it is very likely that the patient will move somewhat during a long examination duration.